1. Field of the Invention
The present invention relates in general to methods and systems for retrieving information, and relates in particular to a method for retrieving information, specified by an information searcher, from a plurality of different database systems which are connected to a communication network.
2. Description of the Related Art
Searching and retrieving information in a database system is carried out by first specifying a target database residing in certain meta-information (known as metadata or schema information, i.e., information on the use of the database and preparing a structured query language (SQL) for) to describe what table to be searched, under what search conditions and what type of information to be retrieved.
When searching for information in a number of databases connected to a communication network, there are search systems that give an impression that the search is being carried out within one database, by having the database manager integrate all the separate sections of meta-information from applicable databases so that there is no need for the information searcher (user) to be aware of the existence of separate databases or their retrieval methods to carry out searches through different databases.
When communicating with databases distributed over several database systems, there are also known methods to work with a structure of the meta-information which is common to all the database systems, so that the user's request is executed by generating a common request to all such systems, and the search results are displayed in a summary table; or when the content of the retrieval information has been decided or when the structure and format of the specified information are given in the retrieval conditions, the specified search content can be analyzed and the target database systems can be selected to lead to the execution of specific search commands.
However, integrated meta-information managed by such conventional multi-databased systems connected to a number of databases are strictly dependent on the data managed by some database management system (DBMS) and are available as an interface to particular sets of data. In using such a retrieval system, the user must be cognizant of the type of data stored, their structures and the format.
Furthermore, there is no assurance that the information available through general meta-information platforms are grouped after interpreting the meaning of the stored data, because data are often selected on the basis of ease of programming or to maintain some consistency in database tables. This situation presents a problem because it is difficult for the user to anticipate the type of information actually being stored unless the user, searching through databases connected to a network, is relatively familiar with the contents of information described in the meta-information.
Further, when searches are conducted through a plurality of distributed database systems, it is necessary that the different meta-information be built on an identical structure, for the retrieval to be successful. Additionally, when working in such a distributed information system, it must be remembered that the system manager is only capable of searching for a set of request items or words recognizable by the DBMS and search results are then reported to correspond to the common items. Therefore, it is difficult for the system manager to respond to individualized request items of the user. Although the user can specify certain database systems to be searched with specific search commands, when the structures and formats of the required information are specified in search content or in search conditions, this is possible only if all the database systems of interest share strictly identical structures, because the existing search methodologies do not permit the user to retrieve information from database systems having different structures.
Therefore, using the conventional information retrieval systems based on present meta-information or schema information offered by an integrally managed platform, the user is required first to interact with an integrated platform of meta-information provided by some DBMS, and then to enter search commands directly applicable to relevant database structures. As the number of database systems connected to a network increases in the future, it becomes increasingly difficult for the user to first understand the contents of the large number of database systems, and then to describe search commands and specify necessary conditions to obtain desired information.
With further advancement anticipated in the communications network, there is a growing desire to connect various database systems to the network so as to more effectively utilize data stored in various database systems. However, even if a technical environment is created so that a large number of databases become accessible in the network, the user still faces a situation of vast amounts of information exceeding his ability to develop proper understanding of the potential information available, resulting in difficulties in retrieving desired information from a widely distributed databases.